1. Field of the Invention
The present invention generally relates to a stereo image display device, and more particularly, to a device capable of displaying a stereo image of a type which does not require the use of stereo viewing spectacles such as including blue and red filters, polarizing plates or liquid crystal shutters.
2. Description of the Prior Art
Except for a stereoscopic holography in which an image is projected onto a vapor, a cloud or a smoke afloat in the air to form a three-dimension image, all of the conventional stereo image display devices that have been developed or actually used are of a design wherein a two-dimension image is so processed as to permit viewers to perceive the image as a three-dimension image. Those stereo image display devices can generally be classified into two types which make use of monocular movement parallax and binocular parallax, respectively.
The system utilizing the motion parallax is known as a Prooflich system and makes use of such a phenomenon that, when an object in motion is viewed, the closer the object is to the viewer, the swifter the motion is perceived and, conversely, the farther the object is, the slower the motion is perceived. The Prooflich system is, however, not employed in practice because, according to this system, the depth cannot sufficiently be expressed, and depth cannot be perceived with respect to an object in still.
The system utilizing the eye-to-eye parallax is based on a vivid perception of the relative distances of objects in space and requires two images displaced relative to each other so that these two images as viewed by the left-hand and right-hand eyes can interact with each other in stereoscopic vision.
The stereo image display device utilizing the eye-to-eye parallax is available in two models which are known as a binocular stereo display device and a multi-eye stereo display device, respectively. The binocular stereo display device requires the use of spectacles to be worn by a viewer, such as a pair of red and blue glass filters, a pair of polarizing plates or a pair of liquid crystal shutters. More specifically, in the case of the binocular stereo display device requiring the use of the liquid crystal shutters, it is necessary that two images to be viewed by the left-hand and right-hand eyes be displayed on a screen of a cathode ray tube alternately for each field so that the images displayed on the screen of the cathode ray tube can be selectively perceived by both eyes for each field through the liquid crystal shutters.
The binocular stereo display device is effective to avoid such problems associated with the generation of a double image (cross-talk) and the reversal of the images to be viewed by respective eyes, but is inconvenient because of the necessity of use of the viewing spectacles to be worn by viewers.
On the other hand, the multi-eye stereo display device is so designed as to separate the images to be viewed by the respective eyes from each other through the use of a partition plate, known as a parallax barrier, or an array of columnar lens elements known as lenticular sheet. The stereo display device utilizing the parallax barrier is disclosed in, for example, a paper entitled "Rittai Terebi ni Tsuite (Discussion on Stereo Television" and published in NHK Giken Geppou Vol. 3, No. 6 (1960) and Vol. 4, No. 5 (1961) and has a problem in that, since imagewise light emitted from the source of the images is intercepted by the parallax barrier, the aperture efficiency tends to be reduced. The stereo display device utilizing the lenticular sheet was discussed during a session of Hoso Bunka Kikin No. 12th Kenkyu Houkokukai, "Sanjigen Eizou to Sanjigen Terebijon (3D Image and 3D Television)", held on Sept. 21, 1987, the principle of which is shown in FIG. 4 of the accompanying drawings. Referring to FIG. 4, an object 1 is photographed by, for example, five television cameras 2a, 2b, 2c, 2d and 2e from different positions. Respective video outputs from the cameras 2a to 2e are reproduced in synchronized relationship with each other by associated video reproducing apparatii 3a, 3b, 3c, 3d and 3e which are operated in synchronism with each other. These video reproducing apparatii 3a to 3e include cathode ray tubes, and imaged reproduced by these cathode ray tubes are in turn projected, in an enlarged scale, by projectors 4a, 4b, 4c, 4d and 4e onto the lenticular sheet 6 through a Fresnel lens 5. Imagewise light so projected from each of the cathode ray tubes is diffused in all directions through the lenticular sheet 6 and viewers can view the reproduced images from the side of the lenticular sheet 6 opposite the Fresnel lens 5.
The Fresnel lens 5 is used to expand the optical distance between the projectors 4a to 4e and the lenticular sheet 6 longer than the actual distance therebetween. Therefore, with the use of the Fresnel lens 5, the distance between the projectors 4a to 4e and the lenticular sheet 6 can be effectively reduced, permitting the device as a whole to be reduced in size.
As is well known to those skilled in the art, the lenticular sheet 6 has a plurality of elongated lens elements laid parallel to each other in closely adjoining relationship. Imagewise light incident upon the elongated lens elements of the lenticular which has been projected from the projectors 4a to 4e and has subsequently passed through the Fresnel lens 5 emerges outwardly therefrom in different directions at an angle determined by the angle of incidence thereof upon the lenticular sheet 6 In other words, the rays of light protected from the projectors 4a, 4b, 4c, 4d and 4e and subsequently emerging from the lenticular sheet 6 travels along respective optical paths as shown by 1a, 1b, 1c, 1d and 1e. Accordingly, the images carried by light traveling along each adjoining optical paths can fall upon the left-hand and right-hand eyes of the viewer 7, permitting the latter to perceive the three-dimension image.
However, it has been found that, since the plural images projected respectively from the projectors 4a to 4e must be formed on the lenticular sheet 6, the use of the Fresnel lens 5 is essential to guide the images towards the elongated lens elements of the lenticular sheet 6, rendering the device as a whole bulky while the use of the projectors 4a to 4e increases the size. Also, the necessity of the images to be guided by the complicated elongated lens elements lowers the productivity and the reliability, making it difficult to employ the device in practice.